Beamforming is a signal processing technique used in antenna arrays for directional signal transmission or reception. “Adaptive beamforming” is a technique in which an array of antennas achieves maximum reception in a specified direction by preferring the arrival of a signal from a desired direction while signals of the same frequency from other directions are suppressed. This is achieved by selectively weighting the signal data of the antenna elements in the array.
Adaptive beam forming is based on the fact that signals originating from different transmitters may occupy the same frequency channel but arrive from different directions. This spatial separation is exploited to separate a desired signal from undesired signals. Spatial selectivity is achieved by using adaptive receive or transmit beam patterns. The beam pattern is formed by adjusting complex weights of the antenna elements so that the beam is directed in a direction of interest. For receiving, information from different antennas is combined in such a way that an expected pattern of radiation is preferentially observed. For transmitting, a beamformer controls the phase and relative amplitude of the signal at each antenna and produces a directional beam in a desired direction.
Beamforming is accomplished either in the frequency domain or in the temporal domain. Beamforming algorithms use a covariance matrix, which carries the spatial and spectral information of the signals.
One adaptive beamforming approach is MVDR (Minumim Variance Distortionless Response), also sometimes also referred to as Capon beamforming. MVDR beamformers achieve good resolution, but the conventional MVDR algorithm has higher complexity due to a full-rank matrix inversion.
Adaptive beamforming when using MVDR applied to large antenna arrays has several hurdles to overcome. A high computational cost associated with a beamforming arrays with many elements is incurred when the beams are formed to cover all space (azimuth and elevation angles). This requires at least as many beams as elements and usually more. Another hurdle is that if the beamformer is to respond quickly to a changing environment then only a limited time is available to re-compute the covariance matrix. Again, this degrades the beamformer white noise intentional signal suppression capability and hence array gain.